A highly effective energy absorber for an aircraft arresting system is described in U.S. Pat. No. 3,172,625. It incorporates a vaned rotor disposed between a pair of vaned staters in a liquid-filled casing. The arresting reaction is coarsely programmed, by the diminishing moment arm of a taped payout line wound on a drum secured to the input drive shaft of the rotor, to provide: free runout after initial contact by the aircraft, substantially constant energy absorption as the moment arm radius and mechanical advantage decrease and final smooth termination as the aircraft and energy absorber slow to rest. Such variation is not, however, as sensitive as is sometime desired, nor does it enable the energy absorber to operate efficiently in conjunction with a wide variety of aircraft. Various devices have been proposed for varying torque in energy absorbers which vary the angle of rotating blades of vanes. Such devices are shown in U.S. Pat. No. 3,168,939 or Italian Pat. No. 527,087 (1955), but are not completely economical, rugged, strong or dependable. An object of this invention is to provide a relatively simple rugged, strong and reliable energy absorber in which the angle of the absorbing blades and the torque-developed are variable.